Biogenic amines as neurotransmitters and neuromodulators

T. Roeder & M. Gewecke

University of Hamburg, Zoological Insitute, Dept Neurophysiology, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany

Biogenic amines are members of a relatively small group of neuroactive compounds known to be important for the generation and control of numerous different behaviours. Most of them are G-protein coupled exerting its physiological role through second-messenger systems. Two biogenic amines, the monoamines octopamine and tyramine are unique for invertebrates as these compounds have no physiological relevance in vertebrates, where their role is occupied from adrenaline and noradrenaline. Especially octopamine is known to play a key role for the generation of numerous behaviours. This physiological importance together with its restriction to invertebrates focused the interest of pharmacologists on corresponding receptors. For octopamine, four different octopamine receptor subtypes where identified. In addition, one tyramine receptor subtype with almost unknown physiological significance was identified. Most octopamine receptors of the nervous system belong to a single class of receptors, the so called class 3 receptors. This receptor is believed to transmit most of the known action of octopaminergic insecticides, e.g. hyperactivity and reduced ability in learning tasks. We focused on the characterisation of this receptor subtype. A number of different agonists and antagonists with high affinity and specificity could be observed. Especially the antagonist epinastine ruled out to be very important for the characterisation of Octopaminergic neurotransmission in insects. Blocking of this kind of neurotransmission was shown to block some predicted effects of octopamine in insects e.g. in the control of visual information processing. Pharmacological studies across different invertebrate phyla revealed features common for all octopamine receptors studied. In addition, we found that octopamine has physiological roles in simple model invertebrates that are comparable to those found in insects.

Index terms: Thrips tabaci, Thrips palmi, TSWV, vector, antibody.

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